System for cooking fibrous material



July 14, 1931. T. DUNBAR SYSTEM FOR COOKING FIBROUS MATERIAL n FiledAug. l, 1929 MHLHXH Enum 83% mkGU @h3 m @D gmnntoz T LDzmbar;

Patented duly 14, l93i UNITED stares THOMAS LEONIIDS DUNBAR, 0FWATERTOW, NEW YORK SYSTEM FOB COOKING FIBROUS MATERIAL Application ledAugust 1, 1929. Serial No. 382,801.

This invention relates to improvements in the cooking or digestion offibrous material'. In digesting brous material, it has been customary toplace wood chips or the like in a digester, cover the same with acidliquor, and then introduce steam steadily from Athe beginning to the endof the cook. I have discovered that aA large proportion of the steam`may be saved, improved pulp may be prepared,- and/great economy may berealized, if the cookin 1s carried out in a certain way.

The gist o my invention resides in the introduction of steamintermittently during the greater portion of the cooking period, and thecutting off of the steam entirely during the latter portion of thecooking period. By such procedure, I have discovered that even thoughthe feeding of the steam to the digester is stopped a few hours beforethe end of the cooking period, that the temperature in the digester willrise as much as 8 C., and this I attribute, either to an exothermicreaction, or to a progressive heat penetration from the center to theouter portion of the mass in the digester. v

The invention will now be described in detail in connection with theaccompanying drawing, which shows a diagrammatic view of an apparatuswith which my method may be practiced.

In the drawing, 1 designates an accumulator to contain pre-conditionedand preheated acid liquor under super-atmospheric pressure. Such liquormay be forced `by means of a pump 2, through a valved conduit 3, intoadigester 4. Only one digester is shown in the drawing, but the presentinvention may be used in connection with any number of digesters, andeach digester will be provided with the usual steam inlet pipe 5, avalved side relief branch 6, and a top relief 7. It is customary withsuch digesters, to use a thermometer 8, a pressure chart 9, a steam flowchart 10, and a recording thermometer 11.

Heretofore, chips or the like, placed in the digester, weresaturatedwith either cold or pre-heated acid liquor, and steam wasintroduced into the digester from the start to the 50 finish of theoperation. During the cooking period, gases, vapors and the like, wererelieved from the digester. In such operation,

the pressure chart and the steam flow chart showed gradual curves fromthe start to the finish of the operation. v v

In accordance with my improved method, after a digester has been filledwith chips or the like, hot acid from the accumulator 1 is pumped intothe digester, and after` the di- -gester is filled with chips and hotacid, I normally run the pump 2 for a few minutes. This causes theliquor to penetrate the chips or the like, and puts a pressure in thedigester without the addition of any steam. As soon as the digester hasbeen brought up to a pressure from l0 to 65 pounds in this way, I beginto admit steam slowly into the bottom of. the digester, through the pipe5, as has been customary in the past, but 1n accordance with my system,very little steam can be admitted at this time, due to the fact that arelatively high pressure already exists in the digester, and the latteris filled with chips. As soon as the steam is turned on, the side relief6 is opened, so that the usual liquors are forced out of the digester,due to the pressure existing therein.

During the time steam is being admitted, and as soon as dry gases can beobtained from the top relief 7, the valve of the side relief 6 is shutoff and from that time on the top relief is used.

As heretofore mentioned, I admit the steam in a different way from thatused heretofore. For example, I admit steam for a certain period of time(say one-half hour), and then Y A 1 shut it off for a subsequent periodof time (say twenty minutes). At the end of this period steam is againadmitted for a certain time, then shut off, and so on. By admittingsteam in this way, so as to produce the stepped chart l0, I actuallyaccomplish a more uniform penetration of the chips with acid. In theusual method, of cooking, the steam is admitted constantly, so that thecurve on the steam flow chart is gradual, instead of stepped, asin mysystem. Furthermore, in the usual method of cooking, the pressureadvances in a uniform' manner, and the penetration of the chips and thedistribution of the heat units throughout the mass of chips and liquorlags considerably behind, What would be expected at any given point, butby stepping up the steam fiow andpressure asl do, I find that in theintervals, `while the steam is shut off, the heat units have a chance tobecome more uniformly distributed, lthereby producing a better pulp andobtaining a higher yield.

In my method, I continue the step by step HOW of the steam until atemperature of about 124or 132 C. has been reached, and I then shut .offthe steam entirely, and finish up the cookwithoutadmitting any moresteam, and in this Way, I also save considerable on the steam, and'produce a better pulp.

i As an eXample,I have discovered that on an eleven hour cook, I cancomplete the cooking process in exactly the same time as heretofore Whensteam was admitted until the cook Was finished; I also find that afterthe steam is shut off, that the recording thermometer used With thedigester, showsthat the temperature continues to raise approximately 8C. This maybe due to an exothermic reaction on it, or be caused byprogressive heat penetration from the center to the outer portion of themass.

The showing ofthe pressure chart 9, and steam flow chart 10 inl theaccompanying drawing-is not -intended to be strictly accurate, but ismerely to indicate what happens due to the step by step fiowof thesteam, until the temperature reaches approximately 12,40 or 132 C., andthen the shutting ofi" of said steam some hours before the end of thecooking period.

From the foregoing it is believed that the operation and advantages ofthe invention may be clearly understood, and it is manifest that changesmay be made in the details vdisclosed, Without departing from the spiritof the invention, as expressed in the claims.

vWhat I claim and desire to secure by Letters Patent is A l. In thedigestion of fibrous material with acid liquor, initially subjecting thefibrous material in a digester tohot acid liquor under pressure, andafterwards intermittently admitting steam to the digester and thuscausing -.the pressure therein to build up step by step.

' In the digestion of fibrous material With acid liquor in a digester,initially subjectingthe fibrous material in the digester to hot acidliquor under pressure, afterwards introducing steam into the digesterfor a period of time` shutting ofiI the steam for a subsequent period oftime. and subsequently again admitting' steam to the digester' foranother period of time. all during the same cooking period.

3. In the diga-'fw of fibrous material `with acid liquor iu a digester,initially subjecting the fibrous material in a digester to hot acidliquor under pressure, and afterwards intermittently admitting steaminto the digester during a single cooking period.

4. In thedigester of fibrous material, placing'such material in adigester chamber, substantially filling ythe chamber with hot acidliquor, then introducing steam intermittently into the acid liquor inthe digester chamber. 5. In the digestion of fibrous material, placingsaid material in a digester chamber, forcing hot acid liquor into thedigester chamber until the pressure therein is at least ten pounds aboveatmospheric, then intermittently introducing steam into the digester.

6. In'the digestion of fibrous material, plac` ing said material inaclosed digester chamber, pumping hot acid liquor into the chamber untilthe pressure therein is at least ten pounds above atmospheric, and thenintermittently introducing steam into the digester.

7.' In the digestion of fibrous material, placing said material in aclosed digester chamber, forcing hot acid liquor into the chamber untila super-atmospheric pressure exists therein, intermittently introducingsteam into the digester, and permitting gases and vapors, to dischargefrom the chamber While the fibrous material is undergoing cooking.

8. In the digestion of fibrous material With acid liquor in a closeddigester chamber, introducing steam into the digester, shutting off thesteam from the digester after the digester has4 reached a certaintemperaturel and at least affew hours before the end of the cookingperiod, and permitting the temperature in the digester to rise after thesteam has been shut ofi' and before the end of the cooking period.

9. In the digestion of fibrous material With acid liquor in a closeddigester, feeding steam into the digester, shutting off the fioW ofsteam to the digester, and permitting the temperature in the digester torise after the steam has been shut off and before the end of the cookingperiod.

10. In the digestion of fibrous material with acid liquor' in a closeddigester, introducing steam into the digester and shutting off the flowof steam after the temperature has` reached a predetermined degree, andpermitting the temperature in the digester to rise approximately 8 C.above said predetermined degree after the steam has been shut oflandbefore the end of the cooking period.

ll. In the digestion of fibrous material with acid liquor in a closedchamber, heating the interior of said chamber to a predetermined degree,and discontinuing the introduction of heat units into the chamber whilepermitting the temperature to rise therein several degrees above thatwhich exists at the timeivhen the introductionof the heat units wasdiscontinued.

l2.v In the digestion el fibrous material, confining such material withacid liquor in a closed chamber, introducing heat units into saidchamber until the temperature therein has reached about 124 C.,discontinuing the introduction of heat units into the chamber, andpermitting the temperature to rise in the chamber about 8 C., after theintroduction of .heat units has been discontinued.

13. In the digestion of brous materia confining a mass of such materialand a pool 10 of acid liquor in a closed digester, introducing steaminto the digester until the temperature therein has reached at least 124C., then shutting olf the fioW of steam to the digester, and permittingthe temperature Within the digester to rise about 8 C., after the steamflow has been shut off.

14. In the digestion of fibrous material, confining a mass of suchmaterial and a pool of acid liquor Within a digester, intermittent- 20.ly introducing steam into the digester until the temperature thereinreaches at least 124 C., then shutting off" the flow of the steam to thedigester, permitting the temperature in the digester to rise severaldegrees after the flow of steam has been shut off, and

then allowing the temperature to fall until the end of the cookingperiod.

l 15. In the digestion of fibrous material, confining a mass of suchmaterial in a digester, forcing hot acid liquor into the digester and incontact with the fibrous maferial until the pressure in the digester isat least ten-pounds above atmospheric, ythen intermittently introducingsteam into the digester until the temperature therein reaches at least120 C., then shutting off the flow of steam to the digester, permittingthe temperature in the. digester to rise after the steam iow has beenshut ofi', and then allow- 40 ing the temperature in the digester tofall to the end of the cooking period.

16. In the digestion of fibrous material, confining a mass of suchmaterial and a pool of hotpacid liquor in a closed digester, pumplinghot acid liquor into the digester and in contact with the fibrousmaterial until the pressure in the digester is above 10 lpoundsatmospheric pressure, then discontinuing the pumping of the acid liquorand introducing steam intermittently into the digester until thetemperature therein has reached at least 124 C., then shutting off theHow of steam to the diglestenand permitting the temperature in t edigester to rise after the steam has been shutoff and before the end ofthe cooking period.

In testimony whereof, I have signed this specification.

THOMAS LEONIDAS DUNBAR.

